1. Field of the Invention
The present invention relates to an internal combustion engine starting control system for vehicles.
2. Description of Related Art
There are known starting control systems and the like, applied to hybrid vehicles which have an internal combustion engine and a motor as driving (force) sources, wherein at least one of the driving forces generated by the internal combustion engine and the motor is transmitted to driving wheels so that the hybrid vehicle moves.
In the first example which is a starting control system, a target rotation speed of the internal combustion engine (i.e., a target engine speed) is corrected in accordance with the degree of increase in the actual engine speed, so as to reduce a period of time necessary for starting the engine and to prevent excessive electric power consumption by the motor (see, for example, Japanese Unexamined Patent Application, First Publication No. 2003-343308).
In the second example which is an internal combustion engine starting system, (i) when a starting operation of the internal combustion engine accomplished by using a starting motor has been completed (i.e., when the rotation speed of the starting motor exceeds a specific threshold), electric power supplied to the starting motor is reduced, or (ii) if an excessive increase in the rotation speed is detected when the starting operation of the internal combustion engine has been completed, electric power is supplied to the starting motor so as to activate the motor (see, for example, Japanese Unexamined Patent Application, First Publication No. H07-119594).
In the third example which is a control system, the internal combustion engine and a starting motor for starting the internal combustion engine are connected via a power transmission device such as a belt, and when the rotation speed of the internal combustion engine (i.e., the engine speed) is lower than a target engine speed, a positive torque is output, and conversely, when the engine speed is higher than the target engine speed, a negative torque is output and the command value for the negative torque has a time constant larger than the time constant of the command value for the positive torque, thereby preventing a sudden change in torque (see, for example, Japanese Unexamined Patent Application, First Publication No. 2003-139028).
However, in the above first and second examples, the electric power supplied to the motor is simply controlled in accordance with the rotation speed of the internal combustion engine or the motor. Therefore, if excessive power is output from a battery (device) provided for communicating electric power with the motor, the battery may be degraded, or other electric equipment devices which receive electric power from the battery may not be suitably operated.
In the above third example, excessive variation in torque is prevented only when the sign of the torque command value is inverted. Therefore, when, for example, the value of the torque is suddenly changed according to the driving state of the vehicle while the sign of the torque command value is maintained (i.e., not inverted), sudden change in torque cannot be prevented.